U.S. patent number 11,095,265 [Application Number 16/831,871] was granted by the patent office on 2021-08-17 for matching circuit and communication device.
This patent grant is currently assigned to MURATA MANUFACTURING CO., LTD.. The grantee listed for this patent is Murata Manufacturing Co., Ltd.. Invention is credited to Hisashi Akiyama.
United States Patent |
11,095,265 |
Akiyama |
August 17, 2021 |
Matching circuit and communication device
Abstract
A matching circuit includes first and second ports, an
autotransformer, and first and second capacitors. The
autotransformer includes a first terminal coupled to a first port,
a second terminal coupled to a second port, and a common terminal
coupled to a reference potential, and includes a series parasitic
inductor and a parallel parasitic inductor. The first capacitor is
coupled in shunt to the second terminal, and defines a low pass
filter together with the series parasitic inductor. The second
capacitor is coupled in series between the first port and the first
terminal, and defines a high pass filter together with the parallel
parasitic inductor.
Inventors: |
Akiyama; Hisashi (Nagaokakyo,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Murata Manufacturing Co., Ltd. |
Nagaokakyo |
N/A |
JP |
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Assignee: |
MURATA MANUFACTURING CO., LTD.
(Kyoto, JP)
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Family
ID: |
1000005743898 |
Appl.
No.: |
16/831,871 |
Filed: |
March 27, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200228086 A1 |
Jul 16, 2020 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2018/034140 |
Sep 14, 2018 |
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Foreign Application Priority Data
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Oct 24, 2017 [JP] |
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JP2017-204886 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
1/04 (20130101); H03H 7/09 (20130101); H03F
1/565 (20130101); H03H 7/38 (20130101); H03F
3/21 (20130101); H03F 2200/387 (20130101); H04B
2001/0408 (20130101) |
Current International
Class: |
H03H
7/38 (20060101); H04B 1/04 (20060101); H03F
1/56 (20060101); H03F 3/21 (20060101); H03H
7/09 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2017-084898 |
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May 2017 |
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JP |
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2011/090080 |
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Jul 2011 |
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WO |
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2012/153691 |
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Nov 2012 |
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WO |
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2014/155873 |
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Oct 2014 |
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WO |
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2015/064138 |
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May 2015 |
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WO |
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2015/076008 |
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May 2015 |
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WO |
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2015/178204 |
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Nov 2015 |
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WO |
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2016/114182 |
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Jul 2016 |
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WO |
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2016/152603 |
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Sep 2016 |
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WO |
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Other References
Official Communication issued in International Patent Application
No. PCT/JP2018/034140, dated Nov. 13, 2018. cited by
applicant.
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Primary Examiner: Chen; Junpeng
Attorney, Agent or Firm: Keating & Bennett, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority to Japanese Patent
Application No. 2017-204886 filed on Oct. 24, 2017 and is a
Continuation Application of PCT Application No. PCT/JP2018/034140
filed on Sep. 14, 2018. The entire contents of each application are
hereby incorporated herein by reference.
Claims
What is claimed is:
1. A matching circuit for matching impedance between a first port
side impedance and a second port side impedance, the matching
circuit comprising: an autotransformer coupled between the first
port and the second port and including a first terminal, a second
terminal and a common terminal; and a second capacitor coupled in
series between the first port and the first terminal and defining a
high pass filter together with a portion of the autotransformer;
wherein the second capacitor is coupled in series with at least a
portion of the autotransformer.
2. The matching circuit according to claim 1, wherein the
autotransformer includes a parallel parasitic inductance component,
and a portion of the autotransformer defines the parallel parasitic
inductance component.
3. The matching circuit according to claim 1, wherein the
autotransformer includes a series parasitic inductance component,
and includes a first capacitor coupled in shunt to the second
terminal and defining a low pass filter together with the series
parasitic inductance component.
4. The matching circuit according to claim 1, wherein the low pass
filter includes a first inductor coupled between the second
terminal and the second port.
5. The matching circuit according to claim 1, wherein one of the
first port and the second port is coupled to a power amplifier, and
another one of the first port and the second port is coupled to an
antenna.
6. The matching circuit according to claim 1, wherein the high pass
filter includes a second inductor coupled between the first
terminal and the common terminal.
7. The matching circuit according to claim 1, wherein one of the
first port and the second port is coupled to a communication
circuit, and another one of the first port and the second port is
coupled to an antenna.
8. The matching circuit according to claim 1, wherein the
autotransformer includes a first coil and a second coil that are
magnetically coupled to each other; the first coil is coupled
between the first terminal and the second terminal; and the second
coil is coupled between the second terminal and the common
terminal.
9. The matching circuit according to claim 8, wherein the
autotransformer is a single component defined by a laminate
including a plurality of insulating base material layers on which
coil conductor patterns are provided; and a coil opening of the
first coil and a coil opening of the second coil overlap each other
when viewed from a lamination direction of the laminate.
10. A communication device comprising: a communication circuit; an
antenna; and a matching circuit coupled between the communication
circuit and the antenna to match impedance between the
communication circuit side impedance and the antenna side
impedance; wherein the matching circuit matches impedances between
a first port and a second port, and includes: an autotransformer
coupled between the first port and the second port and including a
first terminal, a second terminal, and a common terminal; and a
second capacitor coupled in series between the first port and the
first terminal and defining a high pass filter together with a
portion of the autotransformer; and the second capacitor is coupled
in series with at least a portion of the autotransformer.
11. The communication device according to claim 10, wherein the
autotransformer includes a parallel parasitic inductance component,
and a portion of the autotransformer defines the parallel parasitic
inductance component.
12. The communication device according to claim 10, further
comprising a power amplifier coupled between the communication
circuit and the matching circuit.
13. The communication device according to claim 10, wherein the
autotransformer includes a series parasitic inductance component,
and includes a first capacitor coupled in shunt to the second
terminal and defining a low pass filter together with the series
parasitic inductance component.
14. The communication device according to claim 10, wherein the low
pass filter includes a first inductor coupled between the second
terminal and the second port.
15. The communication device according to claim 10, wherein one of
the first port and the second port is coupled to a power amplifier,
and another one of the first port and the second port is coupled to
the antenna.
16. The communication device according to claim 10, wherein the
high pass filter includes a second inductor coupled between the
first terminal and the common terminal.
17. The communication device according to claim 10, wherein one of
the first port and the second port is coupled to the communication
circuit, and another one of the first port and the second port is
coupled to the antenna.
18. The communication device according to claim 10, wherein the
autotransformer includes a first coil and a second coil that are
magnetically coupled to each other; the first coil is coupled
between the first terminal and the second terminal; and the second
coil is coupled between the second terminal and the common
terminal.
19. The communication device according to claim 18, wherein the
autotransformer is a single component defined by a laminate
including a plurality of insulating base material layers on which
coil conductor patterns are provided; and a coil opening of the
first coil and a coil opening of the second coil overlap each other
when viewed from a lamination direction of the laminate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a matching circuit in a
high-frequency circuit such as an antenna matching circuit, and a
communication device including the matching circuit.
2. Description of the Related Art
For example, a matching circuit for matching an output impedance of
a power amplifier to impedance of an antenna is provided between
the power amplifier and the antenna provided in a mobile phone
terminal. Such a matching circuit is disclosed in, for example,
Japanese Unexamined Patent Application Publication No.
2017-84898.
FIG. 15A is a diagram illustrating an example of a matching circuit
shown in Japanese Unexamined Patent Application Publication No.
2017-84898. In FIG. 15A, a power amplifier 40 amplifies a
transmission signal input from a radio frequency integrated circuit
(RFIC) or the like. A matching circuit 30 matches an output
impedance of the power amplifier 40 with impedance of an antenna
1.
In the example shown in FIG. 15A, the matching circuit is
configured with an inductor L31 coupled in series and capacitors
C31 and C32 coupled in shunt. An existing matching circuit of an
output impedance of a general power amplifier is configured with
such an LC filter circuit. Further, as shown in FIG. 15B, the LC
filter circuit may be configured as a multi-stage structure as
required.
The matching circuit of the LC filter circuit configuration has a
narrow frequency range in which good impedance matching is
obtained. Further, since the number of elements necessary for
impedance matching is large, there is a tendency that a loss is
large.
On the other hand, an impedance matching circuit having an
autotransformer structure is disclosed in International Publication
No. WO 2011/090080. FIG. 16 is a circuit diagram of the matching
circuit shown in International Publication No. WO 2011/090080. For
example, a port P1 of the matching circuit is coupled to an output
portion of a power amplifier, and an antenna is coupled to a port
P2 of the matching circuit.
In the matching circuit having an autotransformer structure as
shown in FIG. 16, by determining a value of a parasitic reactance
component of the autotransformer, a transformer ratio can be varied
so as to follow impedance frequency characteristics of the antenna,
and thus impedance matching over a wide band can be achieved.
In a case where such a matching circuit is applied between a power
amplifier and an antenna, for example, a low pass filter or a band
pass filter is often provided in a front or rear stage of the
matching circuit in order to reduce or prevent harmonic components
generated in the power amplifier from being radiated from the
antenna.
Since the filter is configured with an LC circuit, losses caused by
an inductor and a capacitor inevitably increase by providing the
filter. In the high-frequency circuit that requires the impedance
matching circuit and the filter, an increase in loss due to the
provision of the filter is not limited to a circuit provided
between an output portion of the power amplifier and the antenna,
but is common among high-frequency circuits each of which includes
an impedance matching circuit and a filter.
SUMMARY OF THE INVENTION
Preferred embodiments of the present invention provide matching
circuits that each achieve low loss and an impedance matching
function over a wide band and a filter function, and communication
devices including such matching circuits.
A matching circuit according to a preferred embodiment of the
present invention matches impedance between a first port side
impedance and a second port side impedance, and the matching
circuit includes an autotransformer coupled between the first port
and the second port and including a first terminal, a second
terminal and a common terminal, and a first capacitor coupled in
shunt to the second terminal and defining a low pass filter
together with a portion of the autotransformer.
With the above configuration, while impedance matching
characteristics are maintained over a wide band due to the
autotransformer structure, the portion of the autotransformer
defines and functions as a portion of the low pass filter, so that
the low pass filter includes a significantly smaller number of
elements, thus reducing a loss.
In a matching circuit according to a preferred embodiment of the
present invention, for example, the autotransformer includes a
series parasitic inductance component, and the portion of the
autotransformer is the series parasitic inductance component.
In a matching circuit according to a preferred embodiment of the
present invention, for example, the autotransformer includes a
parallel parasitic inductance component, and is provided with a
second capacitor coupled in series between the first port and the
first terminal and defines a high pass filter together with the
parallel parasitic inductance component.
A matching circuit according to a preferred embodiment of the
present invention matches impedance between a first port side
impedance and a second port side impedance, and the matching
circuit includes an autotransformer coupled between the first port
and the second port and including a first terminal, a second
terminal and a common terminal, and a second capacitor coupled in
series between the first port and the first terminal and defining a
high pass filter together with a portion of the
autotransformer.
With the above configuration, while impedance matching
characteristics are maintained over a wide band due to an
autotransformer structure, a portion of the autotransformer defines
and functions as a portion of the high pass filter, so that a high
pass filter includes a substantially smaller number of elements,
thus reducing a loss.
In a matching circuit according to a preferred embodiment of the
present invention, for example, the autotransformer includes a
parallel parasitic inductance component, and the portion of the
autotransformer is the parallel parasitic inductance component.
In a matching circuit according to a preferred embodiment of the
present invention, for example, the autotransformer includes a
series parasitic inductance component, and is provided with a first
capacitor coupled in shunt to the second terminal and defines a low
pass filter together with the series parasitic inductance
component.
In a matching circuit according to a preferred embodiment of the
present invention, the low pass filter may include a first inductor
coupled between the second terminal and the second port. With this
configuration, a required inductance of the inductor coupled in
series is easily determined.
In a matching circuit according to a preferred embodiment of the
present invention, for example, one of the first port and the
second port is coupled to a power amplifier, and the other is
coupled to an antenna.
In a matching circuit according to a preferred embodiment of the
present invention, the high pass filter may include a second
inductor coupled between the first terminal and the common
terminal. With this configuration, a required inductance of the
inductor coupled in parallel is easily determined.
In a matching circuit according to a preferred embodiment of the
present invention, for example, one of the first port and the
second port is coupled to a communication circuit, and the other is
coupled to an antenna.
In a matching circuit according to a preferred embodiment of the
present invention, it is preferable that the autotransformer is
provided with a first coil and a second coil which are magnetically
coupled to each other, the first coil is coupled between the first
terminal and the second terminal, and the second coil is coupled
between the second terminal and the common terminal.
When the autotransformer is configured as described above, the
capacitor (first capacitor) is disposed on a high impedance side,
so that a loss caused by the first capacitor is able to be reduced
or prevented to a small extent. In addition, when the
autotransformer is configured as described above, since the
capacitor (second capacitor) is disposed on a low impedance side,
an equivalent series inductance (ESL) of the capacitor is reduced
or prevented by a negative inductance generated equivalently by the
autotransformer.
In a matching circuit according to a preferred embodiment of the
present invention, it is preferable that the autotransformer is a
single component made by laminating a plurality of insulating base
materials on which coil conductor patterns are formed, and that a
coil opening of the first coil and a coil opening of the second
coil overlap each other when viewed from a direction of the
lamination. With this configuration, the matching circuit is able
to be treated as a chip component, and the impedance matching and
the filter function are able to be provided only by mounting the
matching circuit on a circuit board together with other chip
components.
A communication device according to a preferred embodiment of the
present invention includes a communication circuit, an antenna, and
a matching circuit which is coupled between the communication
circuit and the antenna to match impedance between a communication
circuit side impedance and an antenna side impedance, wherein the
matching circuit matches impedance between a first port side
impedance and a second port side impedance, and includes an
autotransformer coupled between the first port and the second port
and including a first terminal, a second terminal and a common
terminal, and a first capacitor coupled between the second terminal
and the common terminal and defining a low pass filter together
with a portion of the autotransformer.
In a communication device according to a preferred embodiment of
the present invention, for example, the autotransformer includes a
series parasitic inductance component, and a portion of the
autotransformer is the serial parasitic inductance component.
A communication device according to a preferred embodiment of the
present invention includes a communication circuit, an antenna, and
a matching circuit which is coupled between the communication
circuit and the antenna to match impedance between the
communication circuit side impedance and the antenna side
impedance, wherein the matching circuit matches impedance between a
first port side impedance and a second port side impedance, and
includes an autotransformer coupled between the first port and the
second port and including a first terminal, a second terminal and a
common terminal, and a second capacitor coupled in series between
the first port and the first terminal and defining a high pass
filter together with a portion of the autotransformer.
In a communication device according to a preferred embodiment of
the present invention, for example, the autotransformer includes a
parallel parasitic inductance, and a portion of the autotransformer
is the parallel parasitic inductance.
In a matching circuit according to a preferred embodiment of the
present invention, for example, the communication device includes a
power amplifier coupled between the communication circuit and the
matching circuit.
With the above-described configuration, the communication device
with a low loss is obtained while impedance matching between the
communication circuit and the antenna is maintained over a wide
band.
According to preferred embodiments of the present invention,
matching circuits that achieve a low loss and an impedance matching
function over a wide band and a filter function, and communication
devices including the matching circuits are provided.
The above and other elements, features, steps, characteristics and
advantages of the present invention will become more apparent from
the following detailed description of the preferred embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a circuit diagram of a matching circuit 11A according to
a first preferred embodiment of the present invention, and FIG. 1B
is a circuit diagram of a matching circuit 11B according to the
first preferred embodiment of the present invention.
FIGS. 2A to 2C are equivalent circuit diagrams of the matching
circuit 11A shown in FIG. 1A or the matching circuit 11B shown in
FIG. 1B.
FIGS. 3A and 3B are another equivalent circuit diagram of the
matching circuit 11A according to the first preferred embodiment of
the present invention and another equivalent circuit diagram of the
matching circuit 11B according to the first preferred embodiment of
the present invention, respectively.
FIG. 4A is a plan view of each layer of an autotransformer TA or
TB. FIG. 4B is an external perspective view of the autotransformer
TA or TB.
FIG. 5A is a diagram showing frequency characteristics of a passing
loss between a first port P1 and a second port P2 of each of the
matching circuits 11A and 11B, and FIG. 5B is a diagram showing
frequency characteristics of a return loss seen from the first port
P1 of each of the matching circuits 11A and 11B.
FIG. 6A is a circuit diagram of a matching circuit 12A according to
a second preferred embodiment of the present invention, and FIG. 6B
is a circuit diagram of a matching circuit 12B according to the
second preferred embodiment of the present invention.
FIGS. 7A to 7C are equivalent circuit diagrams of the matching
circuit 12A shown in FIG. 6A or the matching circuit 12B shown in
FIG. 6B.
FIGS. 8A and 8B are another equivalent circuit diagram of the
matching circuit 12A according to the second preferred embodiment
of the present invention and another equivalent circuit diagram of
the matching circuit 12B according to the second preferred
embodiment of the present invention, respectively.
FIG. 9A is a diagram showing frequency characteristics of a passing
loss between the first port P1 and the second port P2 of each of
the matching circuits 12A and 12B, and FIG. 9B is a diagram showing
frequency characteristics of a return loss seen from the first port
P1 of each of the matching circuits 12A and 12B.
FIG. 10A is a circuit diagram of a matching circuit 13A according
to a third preferred embodiment of the present invention, and FIG.
10B is an equivalent circuit diagram of the matching circuit
13A.
FIGS. 11A and 11B are diagrams showing frequency characteristics of
a passing loss between the first port P1 and the second port P2 of
the matching circuit 13A, and FIG. 11C is a diagram showing
frequency characteristics of a return loss seen from the first port
P1 of the matching circuit 13A.
FIG. 12A is a circuit diagram of a matching circuit 14A according
to a fourth preferred embodiment of the present invention, and FIG.
12B is an equivalent circuit diagram of the matching circuit
14A.
FIG. 13A is a circuit diagram of another matching circuit 14B
according to the fourth preferred embodiment of the present
invention, and FIG. 13B is an equivalent circuit diagram of the
matching circuit 14B.
FIG. 14 is a block diagram of a communication device 100 according
to a fifth preferred embodiment of the present invention.
FIG. 15A is a diagram illustrating an example of a matching circuit
shown in Japanese Unexamined Patent Application Publication No.
2017-84898 and FIG. 15B is a diagram illustrating an example of a
matching circuit in which an LC filter circuit is formed in a
multistage configuration.
FIG. 16 is a circuit diagram of the matching circuit shown in
International Publication No. WO 2011/090080.
FIG. 17 is a circuit diagram of a matching circuit as a comparative
example with respect to the matching circuit in the third preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, preferred embodiments of the present invention will be
described by using specific examples with reference to the
drawings. In the drawings, the same reference characters are used
to denote the same or corresponding portions. While the preferred
embodiments are shown, for sake of convenience, in a separate
manner in consideration of ease of explanation or understanding of
points, partial substitutions or combinations of configurations
shown in the different preferred embodiments are possible. In the
following description of the second and subsequent preferred
embodiments, description of the same or similar matters as those of
the first preferred embodiment will be omitted, and only different
points will be described. In particular, similar advantageous
effects by similar configurations will not be described in every
preferred embodiment.
First Preferred Embodiment
A first preferred embodiment of the present invention is an example
of an impedance matching circuit having low pass filter
characteristics.
FIG. 1A is a circuit diagram of the matching circuit 11A according
to the first preferred embodiment, and FIG. 1B is a circuit diagram
of the matching circuit 11B according to the first preferred
embodiment. The matching circuits 11A and 11B have a function of
matching impedance between the first port P1 side impedance and the
second port P2 side impedance, and a low pass filter function. The
matching circuit 11A includes an autotransformer TA and a first
capacitor C1. The matching circuit 11B includes the autotransformer
TB and the first capacitor C1.
Each of the autotransformers TA and TB includes a first terminal T1
coupled to the first port P1, a second terminal T2 coupled to the
second port P2, and a common terminal T3 coupled to a reference
potential (ground).
The autotransformer TA of the matching circuit 11A includes a first
coil L1 coupled between a first terminal T1 and a second terminal
T2, and a second coil L2 coupled between the second terminal T2 and
the common terminal T3. The autotransformer TB of the matching
circuit 11B includes a first coil L1 coupled between the first
terminal T1 and a second terminal T2, and the second coil L2
coupled between the first terminal T1 and the common terminal T3.
The first coil L1 and the second coil L2 are coupled to each other
with a coupling coefficient k.
In the matching circuits 11A and 11B, the first capacitor C1 is
coupled in shunt between the second terminal T2 and the ground.
FIGS. 2A to 2C are equivalent circuit diagrams of the matching
circuit 11A shown in FIG. 1A or the matching circuit 11B shown in
FIG. 1B. That is, both of the matching circuits 11A and 11B can be
represented by the equivalent circuit of any one of FIGS. 2A to 2C.
However, in cases where a series parasitic inductor Ls and a
parallel parasitic inductor Lp are on a primary side or on a
secondary side, these inductances are different depending on a
transformer ratio of an ideal transformer.
The autotransformers TA and TB include a series parasitic
inductance component represented by the series parasitic inductor
Ls and a parallel parasitic inductance component represented by the
parallel parasitic inductor Lp. That is, the series parasitic
inductance component represented by the series parasitic inductor
Ls and the parallel parasitic inductance component represented by
the parallel parasitic inductor Lp are a portion of each of the
autotransformers TA and TB. Further, the autotransformers TA and TB
are represented by an ideal transformer IT, the series parasitic
inductor Ls, and the parallel parasitic inductor Lp in an
equivalent circuit in which parasitic components are isolated from
each other.
Here, when a self-inductance of the first coil L1 is represented by
L1, a self-inductance of the second coil L2 is represented by L2, a
mutual inductance of the first coil L1 and the second coil L2 is
represented by M, an inductance of the series parasitic inductor Ls
is represented by Ls, and an inductance of the parallel parasitic
inductor Lp is represented by Lp, the inductance of each parasitic
component is expressed by the following relationships:
M=k (L1*L2)
n=(L1+L2+2M)/(L2+M)
Ls={(1-k.sup.2)L1*L2}/(L1+L2+2M)
Lp=L1+L2+2M
In any of the expressions shown in FIGS. 2A to 2C, a low pass
filter LPF is defined by the first capacitor C1 and the series
parasitic inductor Ls.
That is, since the series parasitic inductor Ls of each of the
autotransformers TA and TB is used as a portion of the low pass
filter LPF, a low pass filter includes a small number of elements.
As a result, compared to a case where an inductor is coupled to the
outside for the low pass filter, for example, a loss caused by the
inductor is not generated, so that the loss can be reduced as a
whole.
FIGS. 3A and 3B are an equivalent circuit diagram of the matching
circuit 11A according to the present preferred embodiment and
another equivalent circuit diagram of the matching circuit 11B
according to the present preferred embodiment, respectively. In
this example, each of the autotransformers TA and TB is represented
by a three-terminal equivalent circuit in which the mutual
inductance M due to magnetic field coupling between the first coil
L1 and the second coil L2 is clearly specified.
When the self-inductance of the first coil L1 is represented by L1,
the self-inductance of the second coil L2 is represented by L2, and
the mutual inductance between the first coil L1 and the second coil
L2 is represented by M in FIGS. 1A and 1B, an inductance of an
inductor La is (L1+M), an inductance of an inductor Lb is (-M), and
an inductance of an inductor Lc is (L2+M) in FIGS. 3A and 3B.
An impedance conversion ratio between the first port P1 and the
second port P2 of the matching circuit 11B shown in FIG. 3B is
(-M+L2+M):(L1+M+L2+M): =L2:(L1+L2+2M).
That is, the first port is a low impedance side, and the second
port P2 is a high impedance side.
According to the matching circuit 11B, since the capacitor (first
capacitor C1) is in parallel on the high impedance side, a current
flowing through the first capacitor C1 is relatively small.
Accordingly, an increase in loss due to the first capacitor C1 is
small.
Next, an example of structures of the autotransformers TA and TB
will be described. FIG. 4A is a plan view of each layer of the
autotransformer TA or TB. FIG. 4B is an external perspective view
of the autotransformer TA or TB. In FIGS. 1A and 1B, a sign of the
autotransformer is separated into TA and TB, but only a circuit
configuration to be coupled to the outside is differentiated
between TA and TB, and the same or substantially the same
components are preferably used.
Each of the autotransformers TA and TB is a surface-mounted chip
component, and includes a plurality of insulating base material
layers including insulating base material layers S1 to S6. Each of
these insulating base material layers is a non-magnetic ceramic
base material layer or a non-magnetic resin base material layer.
Various conductor patterns are provided on the base material layers
S1 to S6. The "various conductor patterns" include not only a
conductor pattern provided on a surface of a base material layer
but also an interlayer coupling conductor. The interlayer coupling
conductor includes not only a via conductor but also an end surface
electrode provided on an end surface of a multilayer body as shown
in FIG. 4B.
The base material S1 corresponds to a mounting surface (the
lowermost layer) of the multilayer body. On the base material layer
S1, the first terminal T1, the second terminal T2, and the common
terminal (ground terminal) T3 are provided.
A loop-shaped conductor pattern L23 preferably of about 11/12
turns, for example, is provided on the base material layer S2. A
loop-shaped conductor pattern L22 preferably of about 9/12 turns,
for example, is provided on the base material layer S3. A
loop-shaped conductor pattern L21 preferably of about 8/12 turns,
for example, is provided on the base material layer S4. The
conductor patterns L21, L22 and L23 coupled in series define the
second coil (the second coil L2 in FIGS. 1A and 1B).
A loop-shaped conductor pattern L12 preferably of about 1/2 turns,
for example, is provided on the base material layer S5. A
loop-shaped conductor pattern L11 preferably of about 8/12 turns,
for example, is provided on the base material layer S6. The
conductor patterns L11 and L12 coupled in series define the first
coil (the first coil L1 in FIGS. 1A and 1B).
In this manner, each of the autotransformers TA and TB is a single
component defined by laminating the plurality of insulating base
material layers on which the coil conductor patterns are provided.
As seen from the direction of the lamination, the autotransformers
TA and TB overlap a coil opening of the first coil L1 and a coil
opening of the second coil L2. Further, preferably, the first coil
L1 and the second coil L2 have the same or substantially the same
winding axis, and inner and outer diameter dimensions thereof are
the same or substantially the same.
With this configuration, the autotransformer can be treated as a
chip component, and the matching circuit can be defined only by
mounting the autotransformer and the first capacitor on a circuit
board.
Next, filter characteristics of the matching circuits 11A and 11B
according to the present preferred embodiment will be described.
FIG. 5A is a diagram showing frequency characteristics of a passing
loss (S21) between the first port P1 and the second port P2 of each
of the matching circuits 11A and 11B, and FIG. 5B is a diagram
showing frequency characteristics of a return loss (S11) seen from
the first port P1 of each of the matching circuits 11A and 11B. In
FIG. 5A, a frequency at which the passing loss is about -3 dB is a
cutoff frequency fc of a low pass filter. The cutoff frequency fc
is higher than an upper limit frequency in a frequency band of a
high-frequency signal input/output to/from the first port P1 and
the second port P2 of each of the matching circuits 11A and 11B.
That is, the high-frequency signal intentionally input from the
first port P1 (second port P2) is hardly attenuated by the low pass
filter, and is output from the second port (first port P1), whereas
a harmonic component (frequency component higher than the
high-frequency signal intentionally input) unintentionally mixed
into the first port P1 (second port P2) is reduced or prevented by
the low pass filter. In other words, the matching circuit according
to the present preferred embodiment includes the low pass filter to
reduce or prevent the harmonic component different from the
high-frequency signal input/output to/from the first port P1 and
the second port P2.
The cutoff frequency fc is preferably lower than twice a
communication frequency. As a result, for example, when a power
amplifier is coupled to one port and an antenna is coupled to the
other port, radiation from the antenna of a harmonic component
caused by distortion characteristics of the power amplifier is
reduced or prevented. In this case, the harmonic component
generated by the distortion characteristics of the power amplifier
corresponds to the harmonic component described above and
unintentionally mixed into the port.
Second Preferred Embodiment
A second preferred embodiment of the present invention is an
example of an impedance matching circuit having high pass filter
characteristics.
FIG. 6A is a circuit diagram of the matching circuit 12A according
to the second preferred embodiment, and FIG. 6B is a circuit
diagram of the matching circuit 12B according to the second
preferred embodiment. The matching circuits 12A and 12B have a
function of matching impedance between the first port P1 side
impedance and the second port P2 side impedance, and a high pass
filter function. The matching circuit 12A includes the
autotransformer TA and a second capacitor C2. The matching circuit
12B includes the autotransformer TB and the second capacitor
C2.
The configurations of the autotransformers TA and TB are as
described in the first preferred embodiment.
In the matching circuits 12A and 12B, the second capacitor C2 is
coupled in series between the first terminal T1 and the first port
P1.
All of FIGS. 7A to 7C are equivalent circuit diagrams of the
matching circuit 12A shown in FIG. 6A or the matching circuit 12B
shown in FIG. 6B. That is, both of the matching circuits 12A and
12B can be represented by the equivalent circuit of any one of
FIGS. 7A to 7C.
In any of the expressions shown in FIGS. 7A to 7C, a high pass
filter HPF includes the second capacitor C2 and the parallel
parasitic inductor Lp.
That is, since the parallel parasitic inductor Lp of the
autotransformers TA and TB are used as a portion of the high pass
filter HPF, the high pass filter can be defined by a small number
of elements. As compared with a case where the inductor is coupled
to the outside for the high pass filter, for example, a loss caused
by the inductor is not generated, thus reducing a loss as a
whole.
FIGS. 8A and 8B are another equivalent circuit diagram of the
matching circuit 12A of the present preferred embodiment and
another equivalent circuit diagram of the matching circuit 12B of
the present preferred embodiment. In this example, each of the
autotransformers TA and TB is represented by a three-terminal
equivalent circuit in which the mutual inductance M due to magnetic
field coupling between the first coil L1 and the second coil L2 is
clearly specified.
In the configuration shown in FIG. 8B, since the second capacitor
C2 is coupled in series to the inductor Lb having an equivalent
negative inductor (-M), an equivalent series inductance (ESL) of
the second capacitor C2 is reduced or prevented by being combined
with the negative inductance (-M). As a result, frequency
dependence is reduced, and the return loss is low over a wide
band.
Next, filter characteristics of the matching circuits 12A and 12B
according to the present preferred embodiment will be described.
FIG. 9A is a diagram showing frequency characteristics of a passing
loss (S21) between the first port P1 and the second port P2 of each
of the matching circuits 12A and 12B, and FIG. 9B is a diagram
showing frequency characteristics of a return loss (S11) seen from
the first port P1 of each of the matching circuits 12A and 12B. In
FIG. 9A, a frequency at which the passing loss is about -3 dB is a
cutoff frequency fc of a high pass filter. The cutoff frequency fc
is preferably lower than a lower limit frequency in a frequency
band of a high-frequency signal input/output to/from the first port
P1 and the second port P2 of each of the matching circuits 12A and
12B. That is, the high-frequency signal intentionally input from
the first port P1 (second port P2) is hardly attenuated by the high
pass filter, and is output from the second port (first port P1),
whereas a subharmonic component (frequency component lower than the
high-frequency signal intentionally input/output) unintentionally
mixed into the first port P1 (second port P2) is reduced or
prevented by the high pass filter. In other words, the matching
circuit of the present preferred embodiment includes the high pass
filter to reduce or prevent the subharmonic component different
from the high-frequency signal input/output to/from the first port
P1 and the second port P2.
The cut-off frequency fc is preferably, for example, equal to or
higher than about 1/2 times the communication frequency. Thus, for
example, when a communication circuit is coupled to one port and an
antenna is coupled to the other port, radiation from the antenna of
a subharmonic component generated in the communication circuit is
reduced or prevented. In this case, the subharmonic component
generated in the communication circuit corresponds to the
subharmonic component unintentionally mixed into the port.
Third Preferred Embodiment
A third preferred embodiment of the present invention is an example
of an impedance matching circuit having band pass filter
characteristics.
FIG. 10A is a circuit diagram of the matching circuit 13A according
to the third preferred embodiment, and FIG. 10B is an equivalent
circuit diagram of the matching circuit 13A. The matching circuit
13A has a function of matching impedance between the first port P1
side impedance and the second port P2 side impedance, and a band
pass filter function. The matching circuit 13A includes the
autotransformer TA, the first capacitor C1, and the second
capacitor C2.
The configuration of the autotransformer TA described above is as
described in the first preferred embodiment.
In the matching circuit 13A, the first capacitor C1 is coupled in
shunt between the second terminal T2 and the ground, and the second
capacitor C2 is coupled in series between the first terminal T1 and
the first port P1.
In FIG. 10B, the low pass filter LPF includes the first capacitor
C1 and the series parasitic inductor Ls. Further, the high pass
filter HPF includes the second capacitor C2 and the parallel
parasitic inductor Lp. The cutoff frequency of the low pass filter
LPF is preferably higher than the frequency band of the
high-frequency signal, and the cutoff frequency of the high pass
filter HPF is lower than the frequency band of the high-frequency
signal. Therefore, band pass filter characteristics are provided
between the first port P1 and the second port P2.
FIGS. 11A and 11B are diagrams showing frequency characteristics of
a passing loss (S21) between the first port P1 and the second port
P2 of the matching circuit 13A, and FIG. 11C is a diagram showing
frequency characteristics of a return loss (S11) seen from the
first port P1 of the matching circuit 13A. In FIGS. 11A to 11C, a
characteristic line P is characteristics of the present preferred
embodiment, and a characteristic line C is characteristics of a
matching circuit of a comparative example.
Here, the matching circuit of the comparative example is shown in
FIG. 17. In FIG. 17, a capacitor C3 and an inductor L3 define the
low pass filter LPF, and a capacitor C4 and an inductor L4 define
the high pass filter HPF. That is, the matching circuit of the
comparative example is obtained by adding, to an impedance matching
circuit by using the autotransformer TA, the low pass filter LPF
and the high pass filter HPF which are separately provided from the
impedance matching circuit.
Values of the respective elements shown in FIG. 10A are preferably,
for example, as follows:
L1=about 0.5 nH
L2=about 7.0 nH
k=about 0.7
C1=about 8.2 pF
C2=about 1.8 pF
Impedance of an RFIC coupled to the first port P1 is preferably,
for example, about 50.OMEGA., and impedance of the antenna coupled
to the second port is preferably, for example, about 3.OMEGA..
Values of the respective elements shown in FIG. 17 are as
follows:
L1=about 0.5 nH
L2=about 7.0 nH
k=about 0.7
C3=about 4.9 pF
C4=about 3.0 pF
L3=about 0.3 nH
L4=about 6.1 nH
Further, a series equivalent resistance (ESR) of each inductor is
calculated by the following equation. R=2.pi.fL/Q
f: frequency
L: inductance
Q values of the inductors L3 and L4 are Q=about 60, and Q values of
the first coil L1 and the second coil are Q=about 30.
An impedance conversion ratio of the autotransformer TA of the
matching circuit 13A according to the present preferred embodiment
is different from an impedance conversion ratio between the first
port P1 and the second port P2. That is, since a predetermined
impedance conversion ratio is obtained as an entire circuit by
adding the first capacitor C1 or the second capacitor C2 defining a
filter, it is possible to reduce not only the number of elements
but also impedance deviation due to the addition of the first
capacitor or the second capacitor for forming the filter, as
compared with a case where a predetermined impedance conversion
ratio is determined for the autotransformer alone and a filter is
added to the autotransformer. In addition, a return loss is
reduced.
With the matching circuit 13A according to the present preferred
embodiment, as shown in FIGS. 11A and 11B, it is possible to pass a
frequency band of, for example, about 1700 MHz to about 2100 MHz
inclusive and to attenuate the other frequency bands. Further, as
shown in FIG. 11B, it was discovered that a passing loss can be
reduced, compared with the matching circuit of the comparative
example.
Also in the third preferred embodiment, the autotransformer may be
configured as the autotransformer TB shown in FIG. 1B and FIG.
6B.
Fourth Preferred Embodiment
In a fourth preferred embodiment of the present invention, an
example of a matching circuit to which an inductor is further
coupled will be shown.
FIG. 12A is a circuit diagram of the matching circuit 14A according
to the fourth preferred embodiment, and FIG. 12B is an equivalent
circuit diagram of the matching circuit 14A. The matching circuit
14A has a function of matching impedance between the first port P1
side impedance and the second port P2 side impedance, and a low
pass filter function. The matching circuit 14A includes the
autotransformer TA, the first capacitor C1, and a first inductor
Ls1.
The configuration of the autotransformer TA described above is as
described in the first preferred embodiment.
In FIG. 12B, the low pass filter LPF includes the series parasitic
inductor Ls, the first inductor Ls1, and the first capacitor
C1.
FIG. 13A is a circuit diagram of another matching circuit 14B
according to the fourth preferred embodiment, and FIG. 13B is an
equivalent circuit diagram of the matching circuit 14B. The
matching circuit 14B has a function of matching impedance between
the first port P1 side impedance and the second port P2 side
impedance, and a high pass filter function. The matching circuit
14B includes the autotransformer TA, the second capacitor C2, and a
second inductor Lp2.
The configuration of the autotransformer TA described above is as
described in the first preferred embodiment.
In FIG. 13B, the high pass filter HPF includes the parallel
parasitic inductor Lp, the second inductor Lp2, and the second
capacitor C2.
As shown in the present preferred embodiment, the first inductor
Ls1 may be coupled to the outside so as to be coupled in series to
the series parasitic inductor Ls of the autotransformer TA.
Similarly, the second inductor Lp2 may be coupled to the outside so
as to be coupled in parallel to the parallel parasitic inductor Lp
of the autotransformer TA.
According to the present preferred embodiment, an inductor coupled
in series in a low pass filter portion is easily set to a required
inductance. Similarly, an inductor coupled in parallel in a high
pass filter portion is easily set to a required inductance.
Also in the fourth preferred embodiment, the autotransformer may be
configured as the autotransformer TB shown in FIG. 1B and FIG.
6B.
Further, band pass filter characteristics may be provided by adding
the second capacitor C2 to the matching circuit 14A shown in FIG.
12A or by adding the first capacitor C1 to the matching circuit 14B
shown in FIG. 13A. Further, the second capacitor C2 and the second
inductor Lp2 may be added to the matching circuit 14A shown in FIG.
12A, or the first capacitor C1 and the first inductor Ls1 may be
added to the matching circuit 14B shown in FIG. 13A.
Fifth Preferred Embodiment
In a fifth preferred embodiment of the present invention, an
example of a communication device will be described.
FIG. 14 is a block diagram of a communication device 100 according
to the fifth preferred embodiment. The communication device 100
according to the present preferred embodiment includes the antenna
1, a matching circuit 10, the power amplifier 40, and an RFIC
(communication circuit) 50. The matching circuit 10 and the power
amplifier 40 are coupled between the antenna 1 and the RFIC
(communication circuit) 50, and the power amplifier 40 is coupled
between the RFIC 50 and the matching circuit 10. Also, a
configuration of the matching circuit 10 is that of the matching
circuit shown in each preferred embodiment described above. The
RFIC 50 includes a transmission circuit for a low band (for
example, about 700 MHz to about 1.0 GHz) and a high band (for
example, about 1.4 GHz to about 2.7 GHz). The antenna 1 preferably
includes, for example, a monopole antenna, an inverted-L antenna,
an inverted-F antenna, and the like corresponding to the low band
and the high band. Note that a reception circuit system is not
shown in FIG. 14.
The elements described above are preferably housed in one housing.
For example, the matching circuit 10, the power amplifier 40, and
the RFIC 50 are mounted on a printed wiring board, and the printed
wiring board is housed in the housing. The antenna 1 may be mounted
on the printed wiring board or may be disposed on an inner surface
of the housing.
With the configuration described above, a communication device with
a low loss can be obtained while maintaining impedance matching
between the communication circuit and the antenna over a wide
band.
While preferred embodiments of the present invention have been
described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing from the scope and spirit of the present invention. The
scope of the present invention, therefore, is to be determined
solely by the following claims.
* * * * *